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COLORATION.
COLORATION.
BY ERNEST A . ELLIOTT, F . Z . S . , F . E . S . ,
etc.
COLOUR depends upon s t r u c t u r e ; hence, where there is no structure, colour is lacking, T h e universally accepted division of the Animal World is into (1) Invertebrata, without backbone, and (2) Vertebrata, with backbone ; b u t from the present point of view it may be divided into (1) Protozoa, with no especial organs, and (2) Organozoa, possessing organs. T h e Protozoa are a sub-kingdom of the Invertebrata, the simplest of which consist of a structureless and colourless mass of protoplasm ; some possess a cell-like pulsating body, called the contractile vesicle, the function of which is not known, and in it we find the first trace of colour, a faint pink. T h e Radiolaria present the first differentiation of parts, a central mass of cells with an external coating; here we find pronounced colours. In Sporiges certain cilia-lined cells suck in water, containing food, and eject the exhausted fluid ; these cells are the first t r u e organs f o u n d in the animal kingdom and are often vividly pigmented. M a n y seaside visitors t o Bawdsey Cliff are familiar with the horny brown tubes attached to shells and stones, Tubiilaria. Their inhabitants show at the orifice a double set of tentacles, which are coloured f r o m pale pink to vivid red. T h e true Jellyfish, Medusa, often display bright hues, arranged along the canals and on the rudimentary eye-spots. U p to this point all the creatures are transparent, with internal tints. Turning now to the Actinozoa (sea Anemones and Corals), we find the body more opaque and the colour applied externally. In the Anemones the colour greatly varies in the same species but the pattern remains constant. T h e column or body is often brightly pigmented or spotted, and the tentacles always of a sharply contrasting hue ; moreover the eye spots, and a zone round t h e body, are almost always azure. Corals are like colonies of single Anemones, b u t with a stony skeleton ; the tentacles protruding tro.m the orifices are always brilliantly coloured, making the w m g coral-reef like a luxurious tropical flower-garden. In t h e ' Jrganpipe Coral (Tubipora musica, Linn.) the t u b e is deep red or crimson, the polyp vividly emerald green ; and, in the Red Coral ot commerce (Corallium nobile, Linn.) the polyp is white. e find then, no colour in structureless P r o t o z o a ; the r u d i mentary organ, where present, slightly decorated. I n transparent
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animals the colour to be applied directly to the organ and internal as canals, or external as eye spots. In opaque animals the colour to be external, and the most highly differentiated parts to be those most strongly pigmented, e.g. tentacles or eye-spots. In the caterpillars of Lepidoptera w e usually find a more or less distinct line running down the centre of the back, corresponding to the dorsal alimentary canal w h i c h lies just below the skin. T h e spiracles are generally marked by spots, often connected by a line T h e s e spots may be repeated in a line above the spiracular line, as in the H a w k - m o t h Deilephila euphorbia : where there is an oblique horn, it is always emphasized in colour, and sometimes the spot beneath it is also oblique ; or it may be repeated in oblique stripes along the body, as in Sphinx ligustri. i he segmentation may be strongly emphasized b y contrasted coloration, as in Tyria (Euchelia) jacobaa and Papilio Machaon. A l l such decoration is clearly structural. Butterflies are found from the Arctic Region to the Equator, on the tops of mountains and in the plains, on the and deserts and amid tropical Vegetation ; they are day-flyers, and mostly brightly coloured. M o t h s are chiefly night-flyers and with sober c o l o u r s ; but the bright Burnets and T i g e r M o t h s are day-flyers and the H a w k M o t h s fly in the e v e n i n g : these all have bnghter coloration than the nocturnal species. T h e upper surface or Butterflies is, as a rule, the seat of the brightest colours the under surface being mottled or patterned to resemble the natural surroundings, w h e n the resting insect closes its wings. ine Orange T i p is most conspicuous in the cabinet, but, when at resi on an umbelliferous plant w i t h its orange tip concealed, tne green-veined under surface renders it inconspicuous. ine brilliant Arevnnis Lathonia, w i t h silver plates on the under siae is also conspicuous in the c a b i n e t ; but it is difficult to see among b r o w n leaves or stones where it often settles in bouth fcuropc, even w h e n marked d o w n to the resting place. T h e wings are covered with scales, formed of t w o or more finely striated plates. T h e pigment consists of granules, placed in ro between the striÂŽ. T h e y may occur on the upper surface o upper membrane, w h e n they are called eptdermal, and, De ng produced on the upper dry epidermis, are permanent not raa , after death : of this nature are the metallic tints of blue, g r e ^ bronze, gold and silver, also the dead blacks and browns an some of the reds. Other granules, called h y p o d e r m a l are formed on the upper surface of the moister middle or 1 ( ; w e r P ' " h e n these show through the epidermis and lade after death the specimen becomes dry : here belong most of the biues, g and yellow, milk-white and orange. C o l o u r may also be ca by interference with the rays of light b y the fine s t n s , . diffraction.
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Colour usually begins with spots, which may spread over a large part of the wing or develope into ocelli or, by coalescence, form bars and stripes. As a familiar case in point, we find our Brimstone butterfly has an orange spot only, which is sometimes elongated into a short streak ; a Continental species Gonepteryx Cleopatra, Linn., has the fore wing orange, with only a narrow yellow border; in others the hind wing also partakes of this extension, and in some Indian species both wings are entirely orange. T h e hind margin of the wings is mostly marked by a border pattern, and there is usually a direct association between the formation of the border and the shape of the margin. Out of our sixty-two Suffolk butterflies, thirty-three have piain hind margin and the border either piain or wanting ; twenty-three have the margin of the fore wing either piain or slightly scalloped, with a slightly scalloped border pattern, the hind wing margin and border pattern slightly scalloped ; and nine have a scalloped margin and border pattern : In Newman's Vanessa Urtica, var. 3 (British Butterflies 1868, p. 52), the outline of the wings is much simpler than in the type form, and the border pattern closely corresponds to it. Another connection between form and colour is found in those with tailed hind wings, for the tail has at its base a spot of pigment brighter than the rest of the wing. Several nervures join at the apex of the discoidal cell, arresting the flow of their contained pigment: this check is marked in many butterflies and most moths by a spot of colour. Albinism, due to the bleaching of the colouring matter, is found with us only in the Outer Hebrides; and Wallace mentions Xanthism or a tendency to yellow, which he found plentifully in insular faunas. Melanism is caused by the expansion of black spots, sometimes covering the whole wings : Biston betularius, '-•> a white moth peppered with black, becomes sometimes entirely black; this form is spreading rapidly throughout Suffolk. Insects, especially white or light coloured species, seem to have a tendency to become melanic in northern and alpine places ; it has been suggested that such darkening in cold regions is for the Purpose of . absorbing heat, which seems probable (cp. L. Tower's 1903 ' Colors, etc., of Coleoptera '). In Mynapoda the decorative patterns are similar to those of Lepidopterous larvae. Among Spiders the primarv scheme of coloration appears as a distinction of the cephalothorax from tne abdomen by a different colour. Blackwell in 1861 enumerates . ~ species of British Spiders, of which 203 have these parts individually coloured. T h e colour pattern on the abdomen, jhough much varied, so greatly resembles the dorsal vessel that ' e s just beneath, that it seems excellent evidence of the connection between colour and structure.
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In Birds the breast is the seat of the greatest functional activity, and frequently vividly tinted. Among Mammalia the axial decoration is very marked. In those showing alternate dark and light bands or spcts (Zebras, some Deer, many Carnivora) we find the region of the spinal column indicated by a dark streak, the flanks striped or spotted along or between the lines of the ribs, and curved lines on Shoulder and hip ; but the pattern and direction of such lines or spots change at the head, neck and every joint of the limbs, and the tips of the ears, nose, tail and feet are distinctively emphasised with colour. In the Badger there is a bulge-shaped mass of coloured hair axially placed near the dorsal and lumbar regions ; Shoulder and loins are well marked. A tendency is arising nowadays to discredit animals' adaptability to environment. M r . Benson's researches into coloration of Peromyscus-mice led him to the inference " that the characters were inherited " and not adapted (Concealing Coloration among Desert Rodents of SW. of U.S.A. : Univ. Californ. Publ. Zool. 1933, xl, p. 1); and Mr. Buxton advocates divesting ourselves " of our belief in protective coloration, at least as far as it is applied to desert a n i m a l s " (Animal Life in Deserts; London, 1928, p. 62). But my own experience, gained chiefly in Australia, indicates just such denizens of the great open spaces as affording striking examples of the truest Protective Resemblance by colour. Colours as a whole may be divided somewhat thus :—1. General coloration, or such as appears to have no special function as colour. For instance, the green hue of leaves which, though chemically useful, seems to have no particular use as colour. 2. Distinctive coloration, i.e. arrangement in patterns or tints corresponding to each species. 3. Protective resemblance, i.e. a system ot coloration which conceals the prey from its foe or the animal from its prey, as the green of caterpillars or the s t r i p e s ot t h e tiger. 4. Mimetic colouring, i.e. resemblance of one animal to another. Always the resemblance of a rare species, which is the food of some animal, to a common nauseous species. 5. Warning colours, i.e. to warn its would-be attackers of its being in some way distasteful. 6. Sexual coloration, i.e. modification of colour in the two sexes, generally in the form of brilliancy in the male. In the case of Insects, it has not yet been remarked how large is the proportion of testaceous or semi-testaceous H y m e n o p t e u among those that are attracted to artificial light. This is illustrated by the species thus captured by our Members durms the past summer in the New Forest, where this p r o p o r t i o n represented by micropterous Alomyia debellator, Fab., Herrn e <> bicolorinus, Gr., Pezomachus zonatus, Fst., fasciatus, Fab. an cautus, Fst., Mesoleptus testaceus, Fab., Perilissus spilonotus, t>t •• Eclytus ornahis and fontinalis, Hlgr., Prionopoda stictica, r a •.
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Labrorhychus clandestinus, Gr., Ophion bombycivorus, Gr. and several parvulus, Kr., Paniscus cristatus, Th., Mesochoriis politiis, Gr., vitticollis and vittator, Hlgr., the Braconids Meteorus albiditarsis, Ct. and deceptor, Wsm., many Macrocentrus abdominalis, Fab. and Rhogas circumscriptus, Nees. Against these, the black or infuscate kinds were merely Platylabus tiigricollis, Wsm., Hemiteles marginatus, Bdg., Pimpla turionellce, var. flavicoxis, Th., and brassicarice, Poda, Lissonota carbonaria, Hlgr., Promethus dorsalis, Hlgr., Angitia apostata, Gr. and claripennis, Th. Much work yet remains to be done respecting the attraction of parasitic Hymenoptera to light, like that of their hosts the light-loving Moths.
SEA-MICE.â&#x20AC;&#x201D;I have recently been investigating Sea-mice of the genus Aphrodita of P. S. Pallas in his Spicilegia Zool. 1766 ; they are found to be marine polycheat Worms, belonging to the group Errantia, though very unwormlike. For the body is generally flattened, oblong or oval with the integument of the back raised into a series of overlapping scales, disposed in two rows ; the head is distinct, bearing both eyes and tentacles as well as a powerful protrusible pharynx or probosis ; the lateral processes of the body called parapodia are large and bear numerous spines, bristles and rudimentary branchiae; of vascular system there seems to be none. The Common Sea-mouse (A aculeata, L.) is by no means infrequent on the more southerly coasts of England, mcluding Suffolk; a very beautiful animal, oval and some nine inches in length, with the dorsal scales or notopodia covered by some iridescent hairs and others forming a feit of silky consistency, which glows in sunlight more resplendently than the Hummingbird's plumage or the most brilliant precious stone. A. borealis and the Porcupine Sea-mouse (Hermione hystrix, Sav.) are the other British kinds, not yet noted in Suffolk ; the latter has its aorsal scales or notopodia exposed and is neither so large nor nlliant as our species. Sea-mice are carnivorous and found under stones at low-water mark or in shallow pools; they are otten thrown on to the shore in great numbers by storms, as in we Aldeburgh case (Trans, supra i, p. 143) mentioned by Dr. Mark i aylor.â&#x20AC;&#x201D;GRAVES LOMBARD, 2 8 D e c .
1933.